The invention relates to a tire pressure detector for motor vehicles.
In a known construction of a tire pressure detector (DE-OS No. 32 43 854), a reference pressure chamber, which is made from a metal housing, is received in a housing enclosure of insulating material which is screwed into a threaded borehole of the wheel rim by means of a threaded projection. The reference pressure chamber is closed in the front toward the tire by means of a switching diaphragm which cooperates with a contact pin in the reference pressure chamber and with an oscillating circuit in the housing enclosure which is connected to the contact pin. The fastening of the reference pressure chamber in the housing enclosure is effected by means of a metal sleeve which is inserted in the housing enclosure in a form-locking manner and which annularly encloses the reference pressure chamber in the area of the switching diaphragm by means of an inwardly curved rim. The housing enclosure of the tire pressure detector is meant to prevent the heat from reaching the reference pressure chamber when the wheel rim is heated and to prevent the gas which is enclosed in the reference pressure chamber from being heated to a greater extent than the compressed air in the tire.
The known solution has the disadvantage that the housing enclosure, which is made of insulating material, can easily be knocked off by the impact of a stone, which leads to a rapid loss of pressure in the tire and, accordingly, to an increased risk. Another disadvantage resides in that the metal sleeve in the housing enclosure clamps the switching diaphragm at the outer border so that tension can occur at the switching diaphragm, which impairs the switching accuracy of the tire pressure detector in an unwanted manner. It is known in another switch construction of the tire pressure detector (DE-OS No. 31 08 998) to weld the switching diaphragm on the outer rim of the reference pressure chamber so that it lies flat without tension; but the metallic reference pressure chamber in the housing enclosure of the tire pressure detector, which housing enclosure is made of insulating material, is held in this location only by means of a torus which can no longer withstand the centrifugal forces to a sufficient extent during temperature fluctuations and high speeds. Under unfavorable circumstances, the reference pressure chamber chan loosen and be thrown out of the housing enclosure into the interior of the tire, which can lead to a destruction of the tire.
The present solution attempts to achieve a secure mechanical fastening of the reference pressure chamber in the housing of the tire pressure detector while simultaneously achieving a favorable thermal communication with the air in the tire.